Handel's "Poro" will certainly never pack in the crowds the way "La Boheme" does - opera seria and da capo arias simply don't have the kind of mass audience you get for consumptive seamstresses and starving poets with tunes by Puccini. But it is, musically at least (the plot is fairly hopeless), a brilliant piece of work, with a dozen magnificent arias and a few that would be top hits in any truly civilized city, as they were in the London of 1731.

Its first American performance, which launched this year's Handel Festival yesterday at the Kennedy Center, was a historic event, and the singers and orchestra under the gifted baton of Stephen Simon presented the music in a style fully worthy of the occasion. American audiences being what they are today, the score was somewhat shortened, with seven numbers omitted and quite a few de capos lopped off in the second act, but the total was perhaps more effective for these changes, though some beautiful music was undoubtedly left out.

To modern ears, the most curious thing about the opera besides the rather formal structure of the da capo arias and the almost mechanical repetition of arias and recitatives, must be the prevalence of treble voices. The lowest voice heard in an aria was that of tenor Henry Price, with two male roles being filled by mezzos Hilda Harris and Beverly Wolff (both appropriately decked out in pantsuits for this concert performance).

Wolff, in the title role of Porus, a king who fought Alexander the Great both on the battlefield and in alove triangle, gave a particularly brilliant performance of uncommonly challenging music. A few of the low notes originally written for a brilliant castrato were beyond her most comfortable range, but the only sign of that was a slight loss of power, not of accuracy.

Sharing top honors in yesterday's performance was soprano Benita Valente. In her music, one can hear what an extraordinary singer Anna Strada (for whom Handel originally wrote the part) must have been, and Valente sang it with exquisite tone and a fine sense of the ornate baroque style. Both she and Wolff should be specially complimented for the excellent ornamentation of their vocal lines.

Handel's orchestral writing for this opera was notable both for the abundance and the brilliance of instrumental interludes. In these, as in all else, Simon conducted with expert musicianship and mastery of a highly specialized style.